A plasma processing apparatus generates a plasma in a chamber which can be used to treat a workpiece supported by a platen in a process chamber. In some embodiments, the chamber in which the plasma is generated is the process chamber. Such plasma processing apparatus may include, but not be limited to, doping systems, etching systems, and deposition systems. In some plasma processing apparatus, ions from the plasma are attracted towards a workpiece. In a plasma doping apparatus, ions may be attracted with sufficient energy to be implanted into the physical structure of the workpiece, e.g., a semiconductor substrate in one instance.
In other embodiments, the plasma may be generated in one chamber, which ions are extracted from, and the workpiece is treated in a different process chamber. One example of such a configuration may be a beam line ion implanter where the ion source utilizes an inductively coupled plasma (ICP) source. The plasma is generally a quasi-neutral collection of ions (usually having a positive charge) and electrons (having a negative charge). The plasma has an electric field of about 0 volts per centimeter in the bulk of the plasma.
Turning to FIG. 1, a block diagram of one exemplary plasma processing apparatus 100 is illustrated. The plasma processing apparatus 100 includes a process chamber 102 defining an enclosed volume 103. A gas source 104 provides a primary dopant gas to the enclosed volume 103 of the process chamber 102 through the mass flow controller 106. A gas baffle 170 may be positioned in the process chamber 102 to deflect the flow of gas from the gas source 104. A pressure gauge 108 measures the pressure inside the process chamber 102. A vacuum pump 112 evacuates exhausts from the process chamber 102 through an exhaust port 110. An exhaust valve 114 controls the exhaust conductance through the exhaust port 110.
The plasma processing apparatus 100 may further includes a gas pressure controller 116 that is electrically connected to the mass flow controller 106, the pressure gauge 108, and the exhaust valve 114. The gas pressure controller 116 may be configured to maintain a desired pressure in the process chamber 102 by controlling either the exhaust conductance with the exhaust valve 114 or a process gas flow rate with the mass flow controller 106 in a feedback loop that is responsive to the pressure gauge 108.
The process chamber 102 may have a chamber top 118 that includes a first section 120 formed of a dielectric material that extends in a generally horizontal direction. The chamber top 118 also includes a second section 122 formed of a dielectric material that extends a height from the first section 120 in a generally vertical direction. The chamber top 118 further includes a lid 124 formed of an electrically and thermally conductive material that extends across the second section 122 in a horizontal direction.
The plasma processing apparatus 100 further includes a source 101 configured to generate a plasma 140 within the process chamber 102. The source 101 may include a RF source 150 such as a power supply to supply RF power to either one or both of the planar antenna 126 and the helical antenna 146 to generate the plasma 140. The RF source 150 may be coupled to the antennas 126, 146 by an impedance matching network 152 that matches the output impedance of the RF source 150 to the impedance of the RF antennas 126, 146 in order to maximize the power transferred from the RF source 150 to the RF antennas 126, 146.
The plasma processing apparatus 100 may also include a bias power supply 190 electrically coupled to the platen 134. The plasma processing system 100 may further include a controller 156 and a user interface system 158. The controller 156 can be or include a general-purpose computer or network of general-purpose computers that may be programmed to perform desired input/output functions. The controller 156 may also include communication devices, data storage devices, and software. The user interface system 158 may include devices such as touch screens, keyboards, user pointing devices, displays, printers, etc. to allow a user to input commands and/or data and/or to monitor the plasma processing apparatus via the controller 156. A shield ring 194 may be disposed around the platen 134 to improve the uniformity of implanted ion distribution near the edge of the workpiece 138. One or more Faraday sensors such as Faraday cup 199 may also be positioned in the shield ring 194 to sense ion beam current. In some embodiments, the Faraday cup 199 may be part of an independently controlled dose sensing system 197 (not shown).
The plasma processing apparatus 100 may also include an optical emission spectrometer (OES) 159. The OES 159 may be used to quantitively measure the wavelengths emitted by the plasma. As atoms become excited, their electrons move from a normal energy level to an excited energy level. Each species of atom has specific energy levels (excited and normal). As an electron of a particular species moves between these specified energy levels, it emits a specific wavelength of energy, much of which is in the visible spectrum. The OES 159 is used to measure these wavelengths and the number of occurrences of each. Based on this data, it is possible to determine which atoms are being ionized, and the relative concentration of each species in the plasma. This information can be transmitted to the controller 156. In some embodiments, the controller 156 may modify various parameters to adjust this measured concentration of ions. In some embodiments, the OES 159 includes an independent controller. In this embodiment, the OES 159 may be used to validate that the ion concentrations within the plasma are within specified levels.
In operation, the gas source 104 supplies a primary dopant gas containing a desired dopant for implantation into the workpiece 138. The source 101 is configured to generate the plasma 140 within the process chamber 102. The source 101 may be controlled by the controller 156. To generate the plasma 140, the RF source 150 resonates RF currents in at least one of the RF antennas 126, 146 to produce an oscillating magnetic field. The oscillating magnetic field induces RF currents into the process chamber 102. The RF currents in the process chamber 102 excite and ionize the primary dopant gas to generate the plasma 140.
The bias power supply 190 provides a pulsed platen signal having a pulse ON and OFF periods to bias the platen 134 and hence the workpiece 138 to accelerate ions 109 from the plasma 140 towards the workpiece 138. The ions 109 may be positively charged ions and hence the pulse ON periods of the pulsed platen signal may be negative voltage pulses with respect to the process chamber 102 to attract the positively charged ions. The frequency of the pulsed platen signal and/or the duty cycle of the pulses may be selected to provide a desired dose rate. The amplitude of the pulsed platen signal may be selected to provide a desired energy. Monitors, such as the OES 159 and the Faraday cups 199, may be used to monitor ion concentration and dosage, respectively.
One drawback of conventional plasma processing is the inability to insure repeatability, such as of the resistance of contacts using diborane (B2H6) for the presilicidation implant. The contact resistance, which is measured ex-situ, post process, has been found to be a function of at least three parameters. The first parameter is the implant order, where wafers that are processed earlier have a greater resistance than those processed later. The second parameter is the chamber history/wall coverage, which represents the amount of material that has become embedded in the walls of the chamber since last cleaning. The third parameter is the implant conditions, such as plasma chemistry, RF power, gas pressure, platen voltage, total ion dose. This third parameter can be specified in the inputs to the process tool (process recipe) and its effects on plasma conditions (properties and composition) can be measured in-situ, in real time, using the monitors described above. However, the other two parameters are not easily measured, and therefore are typically not used to determine implant parameters in real time. Thus, there is still variability between wafers, despite monitoring of implant conditions. Accordingly, there is a need for a plasma processing method that overcomes the above-described inadequacies and shortcomings.